Some weeks ago, I discussed a large phylogenetic study that separated sticklebacks from the seahorses and pipefishes – today I’m going to discuss a phylogenetics paper that zooms in on the relationships between different sticklebacks(and their very closest relatives).

Many of the same scientists from the earlier stickleback phylogeny were involved in this paper, though there is one new face, Yale’s Tom Near, a longtime Wainwright Lab collaborator and former CPB Postdoc.

The group sequenced the mitochondrial genomes of all nine sticklebacks and stickleback relatives, and they also sequenced 11 nuclear genes. They used both maximum-likelihood and Bayesian methods to estimate a phylogenetic tree of sticklebacks.

Here’s what they found:

The mitogenome and nuclear gene data dovetail beautifully, as do the maximum-likelihood and Bayesian methods for each dataset, so there’s every reason to feel confidant about this arrangement of species.

There are a number of interesting results here: Aulorhynchidae, the family that includes the tubesnout, turns out to be paraphyletic – perhaps the Aulorhynchidae should be folded into the family Gasterosteidae and considered proper sticklebacks?

The thing I find the most interesting is the phylogenetic position of Spinachiaspinachia, an elongated stickleback similar in appearance to the tubesnout. The paper suggests that perhaps Spinachia‘s elongate form is the result of convergent evolution.

It’s also worth thinking about the geographical distribution of stickleback in the context of this phylogeny: Spinachia and Apeltes, two Atlantic Ocean-only species, are grouped together, while the most basal stickleback relatives are all found in the North Pacific.

There are some interesting future directions possible here as well. One of Tom’s specialties is using fossil data to calibrate phylogenies, so it’s likely we’ll see a phylogeny in the near future that gives us an idea of the timescales of major stickleback divergence events.